Article 4, Section 2, Clause 1

Document 5

Articles of Confederation, art. 4

Article IV. The better to secure and perpetuate mutual friendship and intercourse among the people of the different states in this union, the free inhabitants of each of these states, paupers, vagabonds and fugitives from justice excepted, shall be entitled to all privileges and immunities of free citizens in the several states; and the people of each state shall have free ingress and regress to and from any other state, and shall enjoy therein all the privileges of trade and commerce, subject to the same duties, impositions and restrictions as the inhabitants thereof respectively, provided that such restriction shall not extend so far as to prevent the removal of property imported into any state, to any other state, of which the Owner is an inhabitant; provided also that no imposition, duties or restriction shall be laid by any state, on the property of the united states, or either of them.

The Founders' Constitution
Volume 4, Article 4, Section 2, Clause 1, Document 5
http://press-pubs.uchicago.edu/founders/documents/a4_2_1s5.html
The University of Chicago Press